How can I pipe stderr, and not stdout?

Question

I have a program that writes information to stdout and stderr, and I need to process the stderr with grep, leaving

Answer 1

You can use the rc shell.

First install the package (it's less than 1 MB).

This an example of how you would discard standard output and pipe standard error to grep in rc:

find /proc/ >[1] /dev/null |[2] grep task

You can do it without leaving Bash:

rc -c 'find /proc/ >[1] /dev/null |[2] grep task'

As you may have noticed, you can specify which file descriptor you want piped by using brackets after the pipe.

Standard file descriptors are numerated as such:

• 0 : Standard input
• 1 : Standard output
• 2 : Standard error